> On Oct 19, 2016, at 9:37 AM, Alex Martini via swift-evolution
> <[email protected]> wrote:
>
>>
>> On Oct 19, 2016, at 4:50 AM, David Goodine via swift-evolution
>> <[email protected] <mailto:[email protected]>> wrote:
>>
>> Hey all,
>>
>> I don’t know if this is really an ‘evolution’ topic per se, and I’m not on
>> Swift Dev, but thought someone here could shed some light on this.
>>
>> Often when developing code, if I need create mode switches (constant Bools)
>> so that I can move back and forth between different features/implementations
>> for testing, developing experimental features, migration, etc. Currently if
>> I write the following:
>>
>> let useFoo = true
>>
>> if useFoo {
>> // Foo code
>> } else {
>> // Non-Foo code
>> }
>
> In your debugging, do you actually need this condition to be evaluated at
> runtime? For example, in the debugger, are you changing the value of useFoo
> at runtime to switch which branch is used?
>
> If not, maybe #if would be better — it makes the decision at compile time. I
> don't get any warnings from the following code:
>
> let useFoo = true
>
> #if useFoo
> print("foo code")
> #else
> print("non-foo code")
> #endif
Sorry, I hit Send too soon. That listing should read:
#if useFoo
print("foo code")
#else
print("non-foo code")
#endif
You switch useFoo on and off by passing "-D useFoo" to the compiler. For
example:
% swift test.swift
non-foo code
% swift -D useFoo test.swift
foo code
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